Mitigating voltage fade in li-rich manganese-based cathodes: a ‘lattice-pillar’ Zn-doping strategy

Lithium- and manganese-rich layered oxides (LLOs) are promising cathode candidates for high-energy-density lithium-ion batteries; however, their practical application is hindered by voltage decay, sluggish Li⁺ diffusion kinetics, and structural instability caused by migration-induced cation disorder. In this work, Zn-doped Li-rich layered cathode materials with the composition LiLi0.2Mn0.57Ni(0.13–x)Co0.1ZnxO2 (x = 0–0.09) were successfully synthesized via a facile and rapid (~ 30 min) microwave-hydrothermal (MH) route followed by calcination. Systematic characterization reveals that Zn substitution, particularly at the optimal doping level of x = 0.07, acts as a “lattice pillar” that stabilizes the layered framework and effectively suppresses the deleterious migration of transition metal ions into the Li⁺ slab. This structural enhancement is corroborated by Rietveld refinement of XRD patterns, which indicates improved hexagonal ordering, an increased c/a ratio, and a reduced cation mixing degree (I(003)/I(104) ratio improvement). Electrochemical measurements demonstrate that the optimized Zn-doped cathode delivers superior performance with a discharge capacity of 198.5 mAh g⁻¹ after 100 cycles (88.1% retention). Notably, electrochemical impedance spectroscopy (EIS) confirms enhanced ionic transport, as evidenced by a marked reduction in charge-transfer resistance (Rct) from 134.3 Ω (undoped) to 52.1 Ω. Furthermore, differential capacity (dQ/dV) analysis verifies that Zn doping mitigates voltage fade by inhibiting the irreversible layered-to-spinel phase transformation. These findings suggest that the microwave-synthesized Zn-doped cathodes offer a robust strategy to improve both the structural integrity and electrochemical kinetics of Li-rich materials.